All the forums keep saying to put the info in the data folders, but the only folder by that name is in the library/application support/uplink section, and when I did so, none of the themes would show up.

If you are running Uplink 1.6.1, then you are not using anything that is released by Introversion. You are either running the Onlink mod, in which case you need to contact the developers of that mod; or you are running the Mac version, in which case you need to contact Ambrosia Software for support.